The menstrual cycle is a complicated process involving many different hormones, women's sex organs and the brain. Two of the most important hormones of the pituitary gland are follicle stimulating hormone (FSH) and leuteinizing hormone (LH). The pituitary gland is a small gland at the base of the brain which controls all the activity of the sexual organs and their development. At the start of each menstrual cycle, the pituitary gland releases FSH, which causes the immature eggs (follicles) to grow. While the follicle is developing, the cells around the egg produce estrogen, which causes the lining of the uterus to grow each month to prepare it for receiving a fertilized egg. Once the follicle has reached a certain size and development milestone, the rising level of estrogen in the blood signals to the pituitary gland that the ovary is ready to release the egg. The pituitary gland then sends out a high level of LH, which likewise signals the ovary to release the egg for ovulation. This is commonly referred to as the “LH surge.” The LH surge in human females occurs about 24 to 36 hours prior to the onset of ovulation and may last about 1 to 2 days (typically the 14th or 15th day of a normal 28-day menstrual cycle). During the LH surge, the concentration of LH is at least 3 times greater than the basal concentration. For instance, in human females, the LH surge level is between about 50 to 200 milli-International Units per milliliter (“mlU/ml) of urine, while the basal level is between about 6 to 13 mlU/ml.
Various tests have been developed that attempt to diagnose the onset of ovulation by detecting the LH surge. One such test kit is the “ClearBlue® Easy Ovulation Test Pack” (Unipath Diagnostics), which involves dipping a test stick into a cup of urine or in midstream urine. The kit consists of a membrane immobilized with antibodies to LH. As urine is wicked up the strip, the presence of LH will lead to the development of the test line. In each test, a control line must develop for the test to be valid. Though highly accurate, urinary LH-based detection devices are hardly convenient. They generally require the collection of a sample or capture of midstream urine for a specified time period. Then, the user must wait between 3 to 5 minutes to learn the results of the test. If a woman wants to test twice a day and works outside the home, this testing methodology may become very inconvenient. It may also be quite costly if women are using the test strips over the course of several months (especially twice a day) to predict the time of greatest fertility.
Due to the problems noted above, various techniques have been developed that attempt to monitor secondary indicators of ovulation. Several reports, for instance, have linked changes in the menstrual cycle with an increase in breath volatile sulfur in women. (Tonzetich, et al. (1978); Queiroz, et al. (2002)). More specifically, at the beginning of menstruation and during ovulation, the production of proteins in saliva increases, thereby providing bacteria with an increased food source. The number of bacteria in saliva may also experience an increase during both menstruation and ovulation. (Prout, et al., (1970)). Because bacteria produce volatile sulfur compounds through enzymatic action on proteins, it is believed that the increase in protein/bacteria levels leads to a corresponding increase in the generation of sulfurous compounds. Various sources have also indicated that a mid-cycle spike of oral volatile sulfur concentration exists in women. (Tonzetich, et al., (1978)). This increase in volatile sulfur compounds in the mid-cycle may thus provide an alternative method to predict ovulation.
Techniques have thus been developed to predict ovulation based on the presence of volatile sulfur compounds. For instance, U.S. Pat. No. 4,119,089 to Preti, et al., which is incorporated herein in its entirety by reference thereto for all purposes, describes a method that involves testing mouth air for volatile sulfur compounds. More specifically, Preti, et al. indicates that volatile sulfur content of mouth air “spikes” approximately 5 to 7 days prior to ovulation and again at the time of ovulation. Preti, et al. mentions several techniques for measuring sulfur content, including gas chromatography, 2,3,5-triphenyltetrazolium chloride (“TPTZ”) colorimetric indicators, or trained animals (e.g., dogs) that can distinguish the volatile sulfur compounds.
Despite the benefits achieved, however, a need for improvement nevertheless remains. A need currently exists, for example, for a technique that more rapidly detects the onset of ovulation in a simple, non-invasive, and inexpensive manner.